1. Field of the Invention
This invention relates to a novel granular crosslinked copolymer, a packing for high-speed liquid chromatography (abbreviated "HLC") comprising this crosslinked copolymer, and to a process for the production thereof. More specifically, this invention relates to a packing for HLC comprising a styrene-divinylbenzene based copolymer having superior ability to separate organic oligomeric substances, and to a process for production thereof.
2. Description of the Prior Art
With a recent advance in the study and commercialization of "oligomers" having a molecular weight of several hundred to several thousand, their structural characteristics have been determined by infrared absorption spectroscopy, ultraviolet absorption spectroscopy, nuclear magnetic resonance spectroscopy, mass spectrometry analysis, etc. However, no satisfactory method has been established for isolating the oligomers as a single chemical species (molecules), and studies of oligomers as a single chemical species have not been fully developed.
Conventional methods for separating oligomers include, for example, distillation, solvent extraction, crystallization, fractional precipitation, centrifugal separation, and liquid chromatography (abbreviated "LC"). The LC method is best among them in view of the relatively broad molecular weight range to which it is applicable, the reduced restriction on chemical stability, and the ability to separate single chemical species.
An especially suitable type of the LC method is gel permeation chromatography (abbreviated "GPC") because it permits separation by the differences in molecular weight. GPC is a type of liquid chromatography in which the speed of development is retarded as solute molecules permeate a solvent held in the pores of a column packing (to be referred to hereinbelow as a "gel"), and separation into the individual molecules is effected according to the size of solute molecules, i.e., the differences in molecular weight. Accordingly, the oligomer molecules are successively separated and flow out from the column in order of decreasing degrees of polymerization, i.e., in order of increasing ease of permeation of the gel. In the chromatogram thus obtained, the distance between peaks is narrower with smaller amounts of effluents.
When the logarithms of the molecular weights of individual molecules separated by GPC and the volumes of the effluent are plotted on the ordinate and the abscissa, a straight line having a negative slope results. Accordingly, with a higher degree of polymerization, it is more difficult to separate the components of an oligomer into a single chemical species.
In recent years, there has been a strong demand for higher speeds of analysis or separation, and the widespread use of HLC instruments has led to the extensive use of high-speed GPC which can perform analysis within several tens of minutes. To make the individual components of an oligomer having a high degree of polymerization separable by high speed GPC, modifications have been made in the operating conditions, and, for example, a recycle method has been suggested which involves repeatedly passing a solute through a column. However, such a method still suffers from various restrictions. For example, long periods of time are still required for the desired analysis or separation, the device required is expensive, or a high degree of experience is required for setting the operating conditions. This is because a column packed with a gel for high speed GPC, which is used in the field of oligomers, does not have sufficient efficiency (e.g., in separating ability). Heretofore, inorganic gels mainly composed of silica and organic synthetic polymeric gels composed of styrene-divinylbenzene have been used as organic solvent-type GPC gels. Among the inorganic gels, none have a calibration curve suitable for separation of oligomers. The gels comprising styrene-divinylbenzene which are obtained by the methods disclosed in U.S. Pat. Nos. 3,322,695 and 3,326,875, do not simultaneously have satisfactory strength and satisfactory separating ability.